Since the genesis of Social Work in Brazil, there is a very close relationship between the pioneers social workers and the youth and child population. The emergence of the profession in Brazil occurs in the middle of a range of social conflicts, which arise the preoccupation with childhood. Such scenario was fertile to the adoption of eugenicist and hygienist sciences, in discourses and in the assistance institutions. This dissertation investigates the connection between such scientific currents and the social workers conceptions and perceptions of that childhood in Rio de Janeiro. This qualitative research adopts a documental methodology and focuses on the city of Rio de Janeiro, from 1940 to 1950. The proposal is to present an analysis based on the undergraduate thesis elaborated by the first social workers graduated in the Instituto Familiar e Social do Rio de Janeiro. The research has shown that the organization of Social Work has its origins in international influences, focused on the control of the working class in general, in which it was already possible to see the preoccupations with childhood. Therefore, it has been established in Distrito Federal in particular, a Social Work that is a result, uppermost, from the control demands of childhood and working class. This becomes very clear in the perceptions about the population assisted, spanned by stigmas and dogmas propagated with the support of eugenicist and hygienist sciences.